Summary

This module uses a rule-based rewriting engine (based on a
regular-expression parser) to rewrite requested URLs on the
fly. It supports an unlimited number of rules and an
unlimited number of attached rule conditions for each rule, to
provide a really flexible and powerful URL manipulation
mechanism. The URL manipulations can depend on various tests,
of server variables, environment variables, HTTP
headers, or time stamps. Even external database lookups in
various formats can be used to achieve highly granular URL
matching.

This module operates on the full URLs (including the
path-info part) both in per-server context
(httpd.conf) and per-directory context
(.htaccess) and can generate query-string
parts on result. The rewritten result can lead to internal
sub-processing, external request redirection or even to an
internal proxy throughput.

Topics

See also

Apache processes a HTTP request in several phases.
A hook for each of these
phases is provided by the Apache API. mod_rewrite uses two of
these hooks: the URL-to-filename translation hook
(used after the HTTP request has been read, but before any
authorization starts) and the Fixup hook (triggered
after the authorization phases, and after the per-directory
config files (.htaccess) have been read, but
before the content handler is activated).

Once a request comes in, and Apache has determined the
appropriate server (or virtual server), the rewrite engine
starts the URL-to-filename translation,
processing the mod_rewrite directives from the
per-server configuration. A few
steps later, when the final data directories are found, the
per-directory configuration directives of mod_rewrite are
triggered in the Fixup phase.

When mod_rewrite is triggered during these two API phases, it
reads the relevant rulesets from its configuration
structure (which was either created on startup, for
per-server context, or during the directory traversal
for per-directory context). The URL rewriting
engine is started with the appropriate ruleset (one or more
rules together with their conditions), and its operation
is exactly the same for both
configuration contexts. Only the final result processing is
different.

The order of rules in the ruleset is important because the
rewrite engine processes them in a particular (not always
obvious) order, as follows: The rewrite engine loops
through the rulesets (each ruleset being made up of RewriteRule directives, with or without
RewriteConds), rule by rule.
When a particular rule is matched, mod_rewrite
also checks the corresponding conditions (RewriteCond
directives). For historical reasons the conditions are given
first, making the control flow a little bit long-winded. See
Figure 1 for more details.

Figure 1:The control flow of the rewrite engine through a
rewrite ruleset

As above, first the URL is matched against the
Pattern of a rule. If it does not match, mod_rewrite immediately stops processing that rule,
and goes on to the next rule. If the Pattern matches,
mod_rewrite checks for rule conditions.
If none are present, the URL will be replaced with a new string,
constructed from the Substitution string, and mod_rewrite goes on to the next rule.

If RewriteConds exist, an
inner loop is started, processing them in the order that they are
listed. Conditions are not matched against the current URL directly.
A TestString is constructed by expanding variables,
back-references, map lookups, etc., against which the
CondPattern is matched. If the pattern fails to match one
of the conditions, the complete set of rule and associated conditions
fails. If the pattern matches a given condition, then matching continues
to the next condition, until no more conditions are
available. If all conditions match, processing is continued
with the substitution of the Substitution string for the URL.

Using parentheses in Pattern or in one of the
CondPatterns causes back-references to be internally
created.
These can later be referenced using the strings $N and
%N (see below), for creating
the Substitution and TestString strings.
Figure 2 attempts to show how the back-references are
transferred through the process for later expansion.

As of Apache 1.3.20, special characters in
TestString and Substitution strings can be
escaped (that is, treated as normal characters without their
usual special meaning) by prefixing them with a backslash ('\')
character. In other words, you can include an actual
dollar-sign character in a Substitution string by
using '\$'; this keeps mod_rewrite from trying
to treat it as a backreference.

This module keeps track of two additional (non-standard)
CGI/SSI environment variables named SCRIPT_URL
and SCRIPT_URI. These contain the
logical Web-view to the current resource, while the
standard CGI/SSI variables SCRIPT_NAME and
SCRIPT_FILENAME contain the physical
System-view.

Notice: These variables hold the URI/URL as they were
initially requested, that is, before any
rewriting. This is important to note because the rewriting process is
primarily used to rewrite logical URLs to physical
pathnames.

The RewriteBase directive explicitly
sets the base URL for per-directory rewrites. As you will see
below, RewriteRule
can be used in per-directory config files
(.htaccess). In such a case, it will act locally,
stripping the local directory prefix before processing, and applying
rewrite rules only to the remainder. When processing is complete, the
prefix is automatically added back to the
path. The default setting is; RewriteBasephysical-directory-path

When a substitution occurs for a new URL, this module has
to re-inject the URL into the server processing. To be able
to do this it needs to know what the corresponding URL-prefix
or URL-base is. By default this prefix is the corresponding
filepath itself. However, for most websites, URLs are NOT
directly related to physical filename paths, so this
assumption will often be wrong! Therefore, you can
use the RewriteBase directive to specify the
correct URL-prefix.

If your webserver's URLs are not directly
related to physical file paths, you will need to use
RewriteBase in every .htaccess
file where you want to use RewriteRule directives.

This seems very complicated, but is in fact
correct Apache internal processing. Because the
per-directory rewriting comes late in the
process, the rewritten request
has to be re-injected into the Apache kernel, as if it
were a new request. (See mod_rewrite technical
details.)
This is not the serious overhead it may seem to be -
this re-injection is completely internal to the
Apache server (and the same procedure is used by
many other operations within Apache).

The RewriteCond directive defines a
rule condition. One or more RewriteCond
can precede a RewriteRule
directive. The following rule is then only used if both
the current state of the URI matches its pattern, and if these conditions are met.

TestString is a string which can contain the
following expanded constructs in addition to plain text:

RewriteRule backreferences: These are
backreferences of the form $N
(0 <= N <= 9), which provide access to the grouped
parts (in parentheses) of the pattern, from the
RewriteRule which is subject to the current
set of RewriteCond conditions..

RewriteCond backreferences: These are
backreferences of the form %N
(1 <= N <= 9), which provide access to the grouped
parts (again, in parentheses) of the pattern, from the last matched
RewriteCond in the current set
of conditions.

These variables all
correspond to the similarly named HTTP
MIME-headers, C variables of the Apache server or
struct tm fields of the Unix system.
Most are documented elsewhere in the Manual or in
the CGI specification. Those that are special to
mod_rewrite include those below.

IS_SUBREQ

Will contain the text "true" if the request
currently being processed is a sub-request,
"false" otherwise. Sub-requests may be generated
by modules that need to resolve additional files
or URIs in order to complete their tasks.

API_VERSION

This is the version of the Apache module API
(the internal interface between server and
module) in the current httpd build, as defined in
include/ap_mmn.h. The module API version
corresponds to the version of Apache in use (in
the release version of Apache 1.3.14, for
instance, it is 19990320:10), but is mainly of
interest to module authors.

THE_REQUEST

The full HTTP request line sent by the
browser to the server (e.g., "GET
/index.html HTTP/1.1"). This does not
include any additional headers sent by the
browser.

REQUEST_URI

The resource requested in the HTTP request
line. (In the example above, this would be
"/index.html".)

REQUEST_FILENAME

The full local filesystem path to the file or
script matching the request.

HTTPS

Will contain the text "on" if the connection is
using SSL/TLS, or "off" otherwise. (This variable
can be safely used regardless of whether or not
mod_ssl is loaded).

Other things you should be aware of:

The variables SCRIPT_FILENAME and REQUEST_FILENAME
contain the same value - the value of the
filename field of the internal
request_rec structure of the Apache server.
The first name is the commonly known CGI variable name
while the second is the appropriate counterpart of
REQUEST_URI (which contains the value of the
uri field of request_rec).

%{ENV:variable}, where variable can be
any environment variable, is also available.
This is looked-up via internal
Apache structures and (if not found there) via
getenv() from the Apache server process.

%{SSL:variable}, where variable is the
name of an SSL environment
variable, can be used whether or not
mod_ssl is loaded, but will always expand to
the empty string if it is not. Example:
%{SSL:SSL_CIPHER_USEKEYSIZE} may expand to
128.

%{HTTP:header}, where header can be
any HTTP MIME-header name, can always be used to obtain the
value of a header sent in the HTTP request.
Example: %{HTTP:Proxy-Connection} is
the value of the HTTP header
``Proxy-Connection:''.

%{LA-U:variable} can be used for look-aheads which perform
an internal (URL-based) sub-request to determine the final
value of variable. This can be used to access
variable for rewriting which is not available at the current
stage, but will be set in a later phase.

For instance, to rewrite according to the
REMOTE_USER variable from within the
per-server context (httpd.conf file) you must
use %{LA-U:REMOTE_USER} - this
variable is set by the authorization phases, which come
after the URL translation phase (during which mod_rewrite
operates).

On the other hand, because mod_rewrite implements
its per-directory context (.htaccess file) via
the Fixup phase of the API and because the authorization
phases come before this phase, you just can use
%{REMOTE_USER} in that context.

%{LA-F:variable} can be used to perform an internal
(filename-based) sub-request, to determine the final value
of variable. Most of the time, this is the same as
LA-U above.

CondPattern is the condition pattern,
a regular expression which is applied to the
current instance of the TestString.
TestString is first evaluated, before being matched against
CondPattern.

Remember:CondPattern is a
perl compatible regular expression with some
additions:

You can prefix the pattern string with a
'!' character (exclamation mark) to specify a
non-matching pattern.

There are some special variants of CondPatterns.
Instead of real regular expression strings you can also
use one of the following:

'<CondPattern' (lexicographically
precedes)
Treats the CondPattern as a plain string and
compares it lexicographically to TestString. True if
TestString lexicographically precedes
CondPattern.

'>CondPattern' (lexicographically
follows)
Treats the CondPattern as a plain string and
compares it lexicographically to TestString. True if
TestString lexicographically follows
CondPattern.

'=CondPattern' (lexicographically
equal)
Treats the CondPattern as a plain string and
compares it lexicographically to TestString. True if
TestString is lexicographically equal to
CondPattern (the two strings are exactly
equal, character for character). If CondPattern
is "" (two quotation marks) this
compares TestString to the empty string.

'-d' (is
directory)
Treats the TestString as a pathname and tests
whether or not it exists, and is a directory.

'-f' (is regular
file)
Treats the TestString as a pathname and tests
whether or not it exists, and is a regular file.

'-s' (is regular file, with
size)
Treats the TestString as a pathname and tests
whether or not it exists, and is a regular file with size greater
than zero.

'-l' (is symbolic
link)
Treats the TestString as a pathname and tests
whether or not it exists, and is a symbolic link.

'-F' (is existing file, via
subrequest)
Checks whether or not TestString is a valid file,
accessible via all the server's currently-configured
access controls for that path. This uses an internal
subrequest to do the check, so use it with care -
it can impact your server's performance!

'-U' (is existing URL, via
subrequest)
Checks whether or not TestString is a valid URL,
accessible via all the server's currently-configured
access controls for that path. This uses an internal
subrequest to do the check, so use it with care -
it can impact your server's performance!

Note

All of these tests can
also be prefixed by an exclamation mark ('!') to
negate their meaning.

You can also set special flags for
CondPattern by appending
[flags]
as the third argument to the RewriteCond
directive, where flags is a comma-separated list of any of the
following flags:

'nocase|NC'
(no case)
This makes the test case-insensitive - differences
between 'A-Z' and 'a-z' are ignored, both in the
expanded TestString and the CondPattern.
This flag is effective only for comparisons between
TestString and CondPattern. It has no
effect on filesystem and subrequest checks.

'ornext|OR'
(or next condition)
Use this to combine rule conditions with a local OR
instead of the implicit AND. Typical example:

Explanation: If you use a browser which identifies itself
as 'Mozilla' (including Netscape Navigator, Mozilla etc), then you
get the max homepage (which could include frames, or other special
features).
If you use the Lynx browser (which is terminal-based), then
you get the min homepage (which could be a version designed for
easy, text-only browsing).
If neither of these conditions apply (you use any other browser,
or your browser identifies itself as something non-standard), you get
the std (standard) homepage.

The RewriteEngine directive enables or
disables the runtime rewriting engine. If it is set to
off this module does no runtime processing at
all. It does not even update the SCRIPT_URx
environment variables.

Use this directive to disable the module instead of
commenting out all the RewriteRule directives!

Note that, by default, rewrite configurations are not
inherited. This means that you need to have a
RewriteEngine on directive for each virtual host
in which you wish to use it.

RewriteMap directives of the type prg
are not started during server initialization if they're defined in a
context that does not have RewriteEngine set to
on

This directive sets the filename for a synchronization
lockfile which mod_rewrite needs to communicate with RewriteMapprograms. Set this lockfile to a local path (not on a
NFS-mounted device) when you want to use a rewriting
map-program. It is not required for other types of rewriting
maps.

The RewriteLog directive sets the name
of the file to which the server logs any rewriting actions it
performs. If the name does not begin with a slash
('/') then it is assumed to be relative to the
Server Root. The directive should occur only once per
server config.

To disable the logging of
rewriting actions it is not recommended to set
Filename to /dev/null, because
although the rewriting engine does not then output to a
logfile it still creates the logfile output internally.
This will slow down the server with no advantage
to the administrator! To disable logging either
remove or comment out the RewriteLog
directive or use RewriteLogLevel 0!

Security

See the Apache Security Tips
document for details on how your security could be compromised if the
directory where logfiles are stored is writable by anyone other than
the user that starts the server.

The choice of different dbm types is available in
Apache 2.0.41 and later

The RewriteMap directive defines a
Rewriting Map which can be used inside rule
substitution strings by the mapping-functions to
insert/substitute fields through a key lookup. The source of
this lookup can be of various types.

The MapName is
the name of the map and will be used to specify a
mapping-function for the substitution strings of a rewriting
rule via one of the following constructs:

${MapName:LookupKey}${MapName:LookupKey|DefaultValue}

When such a construct occurs, the map MapName is
consulted and the key LookupKey is looked-up. If the
key is found, the map-function construct is substituted by
SubstValue. If the key is not found then it is
substituted by DefaultValue or by the empty string
if no DefaultValue was specified.

This is the standard rewriting map feature where the
MapSource is a plain ASCII file containing
either blank lines, comment lines (starting with a '#'
character) or pairs like the following - one per
line.

This is identical to the Standard Plain Text variant
above but with a special post-processing feature: After
looking up a value it is parsed according to contained
``|'' characters which have the meaning of
``or''. In other words they indicate a set of
alternatives from which the actual returned value is
chosen randomly. For example, you might use the following map
file and directives to provide a random load balancing between
several back-end server, via a reverse-proxy. Images are sent
to one of the servers in the 'static' pool, while everything
else is sent to one of the 'dynamic' pool.

Here the source is a binary format DBM file containing
the same contents as a Plain Text format file, but
in a special representation which is optimized for really
fast lookups. The type can be sdbm, gdbm, ndbm, or
db depending on compile-time
settings. If the type is ommitted, the
compile-time default will be chosen. You can create such a
file with any DBM tool or with the following Perl
script. Be sure to adjust it to create the appropriate
type of DBM. The example creates an NDBM file.

Here the source is a program, not a map file. To
create it you can use a language of your choice, but
the result has to be an executable program (either
object-code or a script with the magic cookie trick
'#!/path/to/interpreter' as the first
line).

This program is started once, when the Apache server
is started, and then communicates with the rewriting engine
via its stdin and stdout
file-handles. For each map-function lookup it will
receive the key to lookup as a newline-terminated string
on stdin. It then has to give back the
looked-up value as a newline-terminated string on
stdout or the four-character string
``NULL'' if it fails (i.e., there
is no corresponding value for the given key). A trivial
program which will implement a 1:1 map (i.e.,
key == value) could be:

External rewriting programs are not started if they're defined in a
context that does not have RewriteEngine set to
on

``Keep it simple, stupid'' (KISS).
If this program hangs, it will cause Apache to hang
when trying to use the relevant rewrite rule.

A common mistake is to use buffered I/O on
stdout. Avoid this, as it will cause a deadloop!
``$|=1'' is used above, to prevent this.

The RewriteLock directive can
be used to define a lockfile which mod_rewrite can use to synchronize
communication with the mapping program. By default no such
synchronization takes place.

The RewriteMap directive can occur more than
once. For each mapping-function use one
RewriteMap directive to declare its rewriting
mapfile. While you cannot declare a map in
per-directory context it is of course possible to
use this map in per-directory context.

Note

For plain text and DBM format files the
looked-up keys are cached in-core until the mtime of the
mapfile changes or the server does a restart. This way you can have
map-functions in rules which are used for every
request. This is no problem, because the external lookup only happens
once!

The RewriteOptions directive sets some
special options for the current per-server or per-directory
configuration. The Option strings can be one of the
following:

inherit

This forces the current configuration to inherit the
configuration of the parent. In per-virtual-server context
this means that the maps, conditions and rules of the main
server are inherited. In per-directory context this means
that conditions and rules of the parent directory's
.htaccess configuration are inherited.

MaxRedirects=number

In order to prevent endless loops of internal redirects
issued by per-directory RewriteRules, mod_rewrite aborts
the request after reaching a maximum number of such redirects and
responds with an 500 Internal Server Error. If you really need
more internal redirects than 10 per request, you may increase
the default to the desired value.

AllowAnyURI

When RewriteRule
is used in VirtualHost or server context with
version 2.0.65 or later of httpd, mod_rewrite
will only process the rewrite rules if the request URI is a URL-path. This avoids
some security issues where particular rules could allow
"surprising" pattern expansions (see CVE-2011-3368
and CVE-2011-4317).
To lift the restriction on matching a URL-path, the
AllowAnyURI option can be enabled, and
mod_rewrite will apply the rule set to any
request URI string, regardless of whether that string matches
the URL-path grammar required by the HTTP specification.

Security Warning

Enabling this option will make the server vulnerable to
security issues if used with rewrite rules which are not
carefully authored. It is strongly recommended
that this option is not used. In particular, beware of input
strings containing the '@' character which could
change the interpretation of the transformed URI, as per the
above CVE names.

MergeBase

With this option, the value of RewriteBase is copied from where it's explicitly defined
into any sub-directory or sub-location that doesn't define its own
RewriteBase.
This flag is available for Apache HTTP Server 2.0.65 and later.

The RewriteRule directive is the real
rewriting workhorse. The directive can occur more than once, with
each instance defining a single rewrite rule. The
order in which these rules are defined is important - this is the order
in which they will be applied at run-time.

Pattern is
a perl compatible regular
expression, which is applied to the current URL.
``Current'' means the value of the URL when this rule is
applied. This may not be the originally requested URL,
which may already have matched a previous rule, and have
been altered.

Some hints on the syntax of regular expressions:

Text:. Any single character
[chars] Character class: Any character of the class ``chars''
[^chars] Character class: Not a character of the class ``chars''
text1|text2 Alternative: text1 or text2
Quantifiers:? 0 or 1 occurrences of the preceding text
* 0 or N occurrences of the preceding text (N > 0)
+ 1 or N occurrences of the preceding text (N > 1)
Grouping:(text) Grouping of text
(used either to set the borders of an alternative as above, or
to make backreferences, where the Nth group can
be referred to on the RHS of a RewriteRule as $N)
Anchors:^ Start-of-line anchor
$ End-of-line anchor
Escaping:\char escape the given char
(for instance, to specify the chars ".[]()" etc.)

For more information about regular expressions, have a look at the
perl regular expression manpage ("perldoc
perlre"). If you are interested in more detailed
information about regular expressions and their variants
(POSIX regex etc.) the following book is dedicated to this topic:

In mod_rewrite, the NOT character
('!') is also available as a possible pattern
prefix. This enables you to negate a pattern; to say, for instance:
``if the current URL does NOT match this
pattern''. This can be used for exceptional cases, where
it is easier to match the negative pattern, or as a last
default rule.

Note

When using the NOT character to negate a pattern, you cannot include
grouped wildcard parts in that pattern. This is because, when the
pattern does NOT match (ie, the negation matches), there are no
contents for the groups. Thus, if negated patterns are used, you
cannot use $N in the substitution string!

The substitution of a
rewrite rule is the string which is substituted for (or
replaces) the original URL which Pattern
matched. In addition to plain text, it can include

Back-references are identifiers of the form
$N
(N=0..9), which will be replaced
by the contents of the Nth group of the
matched Pattern. The server-variables are the same
as for the TestString of a RewriteCond
directive. The mapping-functions come from the
RewriteMap directive and are explained there.
These three types of variables are expanded in the order above.

As already mentioned, all rewrite rules are
applied to the Substitution (in the order in which
they are defined
in the config file). The URL is completely
replaced by the Substitution and the
rewriting process continues until all rules have been applied,
or it is explicitly terminated by a
L flag - see below.

There is a special substitution string named
'-' which means: NO
substitution! This is useful in providing
rewriting rules which only match
URLs but do not substitute anything for them. It is commonly used
in conjunction with the C (chain) flag, in order
to apply more than one pattern before substitution occurs.

Additionally you can set special flags for Substitution by
appending [flags]
as the third argument to the RewriteRule
directive. Flags is a comma-separated list of any of the
following flags:

'chain|C'
(chained with next rule)
This flag chains the current rule with the next rule
(which itself can be chained with the following rule,
and so on). This has the following effect: if a rule
matches, then processing continues as usual -
the flag has no effect. If the rule does
not match, then all following chained
rules are skipped. For instance, it can be used to remove the
``.www'' part, inside a per-directory rule set,
when you let an external redirect happen (where the
``.www'' part should not occur!).

'cookie|CO=NAME:VAL:domain[:lifetime[:path]]'
(set cookie)
This sets a cookie in the client's browser. The cookie's name
is specified by NAME and the value is
VAL. The domain field is the domain of the
cookie, such as '.apache.org', the optional lifetime
is the lifetime of the cookie in minutes, and the optional
path is the path of the cookie

'env|E=VAR:VAL'
(set environment variable)
This forces an environment variable named VAR to
be set to the value VAL, where VAL can
contain regexp backreferences ($N and
%N) which will be expanded. You can use this
flag more than once, to set more than one variable. The
variables can later be dereferenced in many situations, most commonly
from within XSSI (via <!--#echo
var="VAR"-->) or CGI ($ENV{'VAR'}).
You can also dereference the variable in a later RewriteCond pattern, using
%{ENV:VAR}. Use this to strip
information from URLs, while maintaining a record of that information.

'forbidden|F' (force URL
to be forbidden)
This forces the current URL to be forbidden - it immediately
sends back a HTTP response of 403 (FORBIDDEN).
Use this flag in conjunction with
appropriate RewriteConds to conditionally block some
URLs.

'gone|G' (force URL to be
gone)
This forces the current URL to be gone - it
immediately sends back a HTTP response of 410 (GONE). Use
this flag to mark pages which no longer exist as gone.

'last|L'
(last rule)
Stop the rewriting process here and don't apply any more
rewrite rules. This corresponds to the Perl
last command or the break command
in C. Use this flag to prevent the currently
rewritten URL from being rewritten further by following
rules. For example, use it to rewrite the root-path URL
('/') to a real one, e.g.,
'/e/www/'.

'next|N'
(next round)
Re-run the rewriting process (starting again with the
first rewriting rule). This time, the URL to match is no longer
the original URL, but rather the URL returned by the last rewriting rule.
This corresponds to the Perl next command or
the continue command in C. Use
this flag to restart the rewriting process -
to immediately go to the top of the loop.Be careful not to create an infinite
loop!

'nocase|NC'
(no case)
This makes the Pattern case-insensitive,
ignoring difference between 'A-Z' and
'a-z' when Pattern is matched against the current
URL.

'noescape|NE'
(no URI escaping of
output)
This flag prevents mod_rewrite from applying the usual URI
escaping rules to the result of a rewrite. Ordinarily,
special characters (such as '%', '$', ';', and so on)
will be escaped into their hexcode equivalents ('%25',
'%24', and '%3B', respectively); this flag prevents this
from happening. This allows percent symbols to appear in
the output, as in

RewriteRule /foo/(.*) /bar?arg=P1\%3d$1 [R,NE]

which would turn '/foo/zed' into a safe
request for '/bar?arg=P1=zed'.

'nosubreq|NS' (
not for internal
sub-requests)
This flag forces the rewrite engine to skip a
rewrite rule if the current request is an internal
sub-request. For instance, sub-requests occur internally
in Apache when mod_include tries to find out
information about possible directory default files
(index.xxx). On sub-requests it is not
always useful, and can even cause errors, if
the complete set of rules are applied. Use this flag to
exclude some rules.
To decide whether or not to use this rule: if you
prefix URLs with CGI-scripts, to force them to be
processed by the CGI-script, it's likely that you
will run into problems (or significant overhead) on
sub-requests. In these cases, use this flag.

'proxy|P' (force
proxy)
This flag forces the substitution part to be internally
sent as a proxy request and immediately (rewrite
processing stops here) put through the proxy module. You must make
sure that the substitution string is a valid URI
(typically starting with
http://hostname) which can be
handled by the Apache proxy module. If not, you will get an
error from the proxy module. Use this flag to achieve a
more powerful implementation of the ProxyPass directive,
to map remote content into the namespace of the local
server.

'passthrough|PT'
(pass through to next
handler)
This flag forces the rewrite engine to set the
uri field of the internal
request_rec structure to the value of the
filename field. This flag is just a hack to
enable post-processing of the output of
RewriteRule directives, using
Alias, ScriptAlias,
Redirect, and other directives from
various URI-to-filename translators. For example, to rewrite
/abc to /def using
mod_rewrite, and then
/def to /ghi using
mod_alias:

RewriteRule ^/abc(.*) /def$1 [PT]
Alias /def /ghi

If you omit the PT flag,
mod_rewrite will rewrite
uri=/abc/... to
filename=/def/... as a full API-compliant
URI-to-filename translator should do. Then
mod_alias will try to do a
URI-to-filename transition, which will fail.

Note: You must use this flag if you want to
mix directives from different modules which allow
URL-to-filename translators. The typical example
is the use of mod_alias and
mod_rewrite.

'qsappend|QSA'
(query string
append)
This flag forces the rewrite engine to append a query
string part of the substitution string to the existing string,
instead of replacing it. Use this when you want to add more
data to the query string via a rewrite rule.

'redirect|R
[=code]' (force redirect)
Prefix Substitution with
http://thishost[:thisport]/ (which makes the
new URL a URI) to force a external redirection. If no
code is given, a HTTP response of 302 (MOVED
TEMPORARILY) will be returned. If you want to use other response
codes in the range 300-400, simply specify the appropriate number
or use one of the following symbolic names:
temp (default), permanent,
seeother. Use this for rules to
canonicalize the URL and return it to the client - to
translate ``/~'' into
``/u/'', or to always append a slash to
/u/user, etc.Note: When you use this flag, make
sure that the substitution field is a valid URL! Otherwise,
you will be redirecting to an invalid location. Remember
that this flag on its own will only prepend
http://thishost[:thisport]/ to the URL, and rewriting
will continue. Usually, you will want to stop rewriting at this point,
and redirect immediately. To stop rewriting, you should add
the 'L' flag.

'skip|S=num'
(skip next rule(s))
This flag forces the rewriting engine to skip the next
num rules in sequence, if the current rule
matches. Use this to make pseudo if-then-else constructs:
The last rule of the then-clause becomes
skip=N, where N is the number of rules in the
else-clause. (This is not the same as the
'chain|C' flag!)

'type|T=MIME-type'
(force MIME type)
Force the MIME-type of the target file to be
MIME-type. This can be used to
set up the content-type based on some conditions.
For example, the following snippet allows .php files to
be displayed by mod_php if they are called with
the .phps extension:

RewriteRule ^(.+\.php)s$ $1 [T=application/x-httpd-php-source]

Home directory expansion

When the substitution string begins with a string
resembling "/~user" (via explicit text or backreferences), mod_rewrite performs
home directory expansion independent of the presence or configuration
of mod_userdir.

This expansion does not occur when the PT
flag is used on the RewriteRule
directive.

Note: Enabling rewrites in per-directory context

To enable the rewriting engine
for per-directory configuration files, you need to set
``RewriteEngine On'' in these files
and ``Options
FollowSymLinks'' must be enabled. If your
administrator has disabled override of
FollowSymLinks for a user's directory, then
you cannot use the rewriting engine. This restriction is
needed for security reasons.

Note: Pattern matching in per-directory context

Never forget that Pattern is
applied to a complete URL in per-server configuration
files. However, in per-directory configuration files, the
per-directory prefix (which always is the same for a specific
directory) is automatically removed for the pattern matching
and automatically added after the substitution has been
done. This feature is essential for many sorts of rewriting -
without this, you would always have to match the parent
directory which is not always possible.

There is one exception: If a substitution string
starts with ``http://'', then the directory
prefix will not be added, and an
external redirect or proxy throughput (if flag
P is used) is forced!

Note: Substitution of Absolute URLs

When you prefix a substitution field with
http://thishost[:thisport],
mod_rewrite will automatically strip that
out. This auto-reduction on URLs with an implicit external redirect
is most useful in combination with
a mapping-function which generates the
hostname part.

Remember: An unconditional external
redirect to your own server will not work with the prefix
http://thishost because of this feature. To
achieve such a self-redirect, you have to use the
R-flag.

Note: Query String

The Pattern will not be matched against the query string.
Instead, you must use a RewriteCond with the
%{QUERY_STRING} variable. You can, however, create
URLs in the substitution string, containing a query string
part. Simply use a question mark inside the substitution string, to
indicate that the following text should be re-injected into the
query string. When you want to erase an existing query string,
end the substitution string with just a question mark. To
combine a new query string with an old one, use the
[QSA] flag.